Heat is transferred by radiation, conduction or convention. Insulation reduces the rate of heat flow from a warm source, such as the warm interior of a building to a cold exterior in the winter or from a warm exterior to the cool interior of a building in the summer, by interfering with and retarding radiant heat transfer and conduction of heat through solid materials. The resistance to heat flow can be increased by providing thicker walls and less heat conductive wall substrates. All materials such as wood, plaster, dry-wall, glass, glass fiber, closed-cell, and open-cell foam, and air spaces transfer heat, albeit at different rates of heat transfer.
The slower the rate of heat flow, the better the “R-value”, which is a measure of the resistance to heat flow across a one-inch thickness of a material. For example, enclosed air has an approximate R-value of 1.0, near-vacuum has an approximate R-value of 40, metal has an approximate R-value of 0.2, glass fiber has an approximate R-value of 2.8 to 3.0, extruded styrofoam™ has an approximate R-value of 4.3, and closed-cell air bubbles, known as bubble pack, has an approximate R-value of 1.
U.S. Pat. No. 7,056,575 issued Jun. 6, 2006 discloses a multi-layer insulation comprised of a pair of bubble-pack insulation sheets laminated on both sides of a polyethylene film, and a pair of aluminum foil films adhesively mounted on the outer surfaces of the bubble-pack sheets. The closed cells of the bubble pack are filled with air.
Canadian Patent No. 2,067,683 issued Mar. 1, 1994 discloses a flexible insulation having a central section composed of air-bubble cushioning material having a layer of aluminium foil extruded onto each side of the cushioning material for use in hockey rinks.